Data communication systems are known for the conveyance of digital information over a communication path such as a microwave or cable path. Digital information is generally provided to the system at a predetermined data rate, and the system is synchronized to and operative only at the selected rate to transmit a digital signal over the communication path and to recover digital data at the receiving end. In order to provide synchronization with a particular data rate, appropriate clock or timing apparatus must be provided. In addition, synchronous encoding apparatus must often be provided to translate an input signal to a form suitable for transmission, with similar decoding apparatus provided for translating a received data signal to an intended output format. In known systems operative only at a specified clock rate, a change in the data rate would necessitate physical modification of the apparatus to be operative at the different clock rate.